title: Structural analysis of the Mn(IV)/Fe(III) cofactor of Chlamydia trachomatis ribonucleotide reductase by extended X-ray absorption fine structure spectroscopy and density functional theory calculations.
abstract: The class Ic ribonucleotide reductase from Chlamydia trachomatis ( Ct) uses a stable Mn(IV)/Fe(III) cofactor to initiate nucleotide reduction by a free-radical mechanism. Extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculations are used to postulate a structure for this cofactor. Fe and Mn K-edge EXAFS data yield an intermetallic distance of approximately 2.92 A. The Mn data also suggest the presence of a short 1.74 A Mn-O bond. These metrics are compared to the results of DFT calculations on 12 cofactor models derived from the crystal structure of the inactive Fe 2(III/III) form of the protein. Models are differentiated by the protonation states of their bridging and terminal OH X ligands as well as the location of the Mn(IV) ion (site 1 or 2). The models that agree best with experimental observation feature a mu-1,3-carboxylate bridge (E120), terminal solvent (H 2O/OH) to site 1, one mu-O bridge, and one mu-OH bridge. The site-placement of the metal ions cannot be discerned from the available data.
authors.affiliation: Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Jarod M
authors.initials: JM
authors.lastname: Younker
authors.forename: Courtney M
authors.initials: CM
authors.lastname: Krest
authors.forename: Wei
authors.initials: W
authors.lastname: Jiang
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
authors.forename: Michael T
authors.initials: MT
authors.lastname: Green
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002692:Chlamydia trachomatis / Q000201:enzymology*; D003067:Coenzymes / Q000737:chemistry* / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D055668:Photochemical Processes; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D003067:Coenzymes; D005290:Ferric Compounds; D008345:Manganese; D012264:Ribonucleotide Reductases; C108427:ribonucleotide reductase R2 subunit